Question

1. if the net force is zero, the object must:

a. accelerate
b. remain at rest only
c. have constant velocity
d. fall downward

1. a 10 - kg object has a weight of approximately:

a. 1 n
b. 9.8 n
c. 98 n
d. 980 n

1. the normal force acts:

a. parallel to the surface
b. perpendicular to the surface
c. opposite to velocity
d. upward only

Explanation:

11.

Step1: Recall Newton's first law

Newton's first law states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. If the net force \(F_{net}=0\), then from \(F = ma\) (Newton's second law \(F\) is force, \(m\) is mass and \(a\) is acceleration), \(a=\frac{F_{net}}{m}=0\).

Step2: Analyze each option

• Option A: If \(a = 0\), the object does not accelerate. So A is wrong.
• Option B: The object can be in motion with constant velocity (not just at rest). So B is wrong.
• Option C: Since \(a = 0\), the velocity \(v\) is constant (\(a=\frac{\Delta v}{\Delta t}\), if \(a = 0\), \(\Delta v=0\)). So C is correct.
• Option D: There is no reason for the object to fall downward specifically. So D is wrong.

12.

Step1: Use the formula for weight

The weight \(W\) of an object is given by \(W=mg\), where \(m\) is the mass of the object and \(g = 9.8\ m/s^{2}\) (acceleration due to gravity). Given \(m = 10\ kg\) and \(g=9.8\ m/s^{2}\).

Step2: Calculate the weight

Substitute the values into the formula: \(W=10\times9.8=98\ N\)

• Option A: \(1N\) is incorrect.
• Option B: \(9.8N\) is for \(m = 1\ kg\).
• Option C: \(98N\) is correct (\(W=mg=10\times9.8\)).
• Option D: \(980N\) is for \(m = 100\ kg\) (if \(g = 9.8\ m/s^{2}\)).

13.

Step1: Recall the definition of normal force

The normal force \(N\) is the force exerted by a surface on an object. It acts perpendicular to the surface.

Step2: Analyze each option

• Option A: Parallel to the surface is the frictional force (in some cases), not the normal force. So A is wrong.
• Option B: By definition, the normal force acts perpendicular to the surface. So B is correct.
• Option C: Opposite to velocity is the drag force (in fluid - motion or frictional force in some kinematic cases), not the normal force. So C is wrong.
• Option D: It's not always upward. For example, if an object is on an inclined plane, the normal force is perpendicular to the plane (not necessarily upward). So D is wrong.

Answer:

1. C. Have constant velocity
2. C. 98 N
3. B. Perpendicular to the surface